1. Field of the Invention
The invention relates generally to a method of manufacturing a contact plug in a semiconductor device. More particularly, the present invention relates to a method of manufacturing a contact plug in a semiconductor device, which can reduce the resistance of a contact plug by preventing reduction in the impurity concentration of the contact plug formed by selective epitaxial growth (SEG) method.
2. Description of the Prior Art
Using a plug select growth technology in a semiconductor device has been highly appreciated in view of reduction in cell size and simplification of process. In developing a DRAM device of more than 1 G bits, however, in order to use the SEG process for forming a bit-line contact and a capacitor storage contact, the process condition are critical.
In a DRAM device of more than 1 G bits, it is difficult to apply polysilicon that has been usually used as a contact plug since its contact area is miniaturized. As the area of the contact is reduced, the contact resistance is further increased. Thus, there is a difficulty in using polysilicon as a contact plug. In other words, in case of using a plug SEG that is grown in the same single crystal to the silicon substrate, an increase in resistance depending on reduction in the contact area can be prohibited by minimizing an interfacial resistance with the silicon.
In case of SEG, however, phosphorous (P) is not doped by more than 1E20 atoms/cc, whereas the doping concentration of phosphorous (P) is more than 1E21 atoms/cc in polysilicon. This will cause increase in resistance when the SEG plug process is actually used.
The disclosed method is a method of manufacturing a contact plug in a semiconductor device capable of improving an electrical characteristic of the device, by which an impurity such as phosphorous (P) is thermally doped in-situ to increase the concentration of the impurity during the process of forming a contact plug by SEG method and after it is formed, in order to prevent an increase in resistance due to reduction in the impurity concentration of a contact plug formed by SEG method.
The disclosed method comprises the steps of growing a SEG contact plug on a semiconductor substrate in which various components for forming a semiconductor device is formed by means of selective growth method, thermally doping the impurity during when the SEG contact plug is grown, and thermally doping the impurity after the SEG contact plug is grown.
In the above step, the SEG contact plug is formed using a polysilicon layer. The thermal doping is performed using H2 and PH3 gas at a temperature ranging from about 800xc2x0 C. to about 950xc2x0 C. under a pressure ranging from about 20 Torr to about 200 Torr. The PH3 gas is diluted by about 1% to about 10% using H2 gas and is then supplied at a flow rate ranging from about 100 sccm to about 5000 sccm. The input flow of said H2 gas ranges from about 1 slm to about 10 slm.
The thermal doping during when the contact plug is formed is implemented after an initial contact plug formation to an initial thickness ranging from about 100 xc3x85 to about 500 xc3x85 by means of the selective growth method.